This invention relates to a rotary damper and in particular to improvements in a vane type rotary damper.
Rotary dampers are sometimes used in steering mechanisms for newer motorcycles. A rotary damper can be useful in damping front wheel oscillation while the vehicle is moving. Such a use is described, for example, in Japanese Laid Open Patent Application No. 2001-99208.
A rotary damper of the same general type as that described in the Japanese publication is depicted schematically in FIG. 2 that accompanies this specification. The damper includes a left oil chamber R1 and a right oil chamber R2, which are separated from one another by a vane 2 and located inside a housing 1. The vane 2 has an orifice 2a through it, which allows communication between the left oil chamber R1 and the right oil chamber R2 through the orifice 2a. A damping effect is generated as oil flows between the left and right orifices R1 and R2 as their relative sizes change as the vane 2 moves back and forth inside the chamber.
Reference characters 4, 5, 6, and 7 are used in the figures to indicate parts that control the flow of operating oil between the left oil chamber R1 and the right oil chamber R2 as the oil passes through a single damping valve 10 and a relief valve V via bypasses in the form of passages L1 and L2. An accumulator A is provided in communication with the passages L1 and L2 in order to control changes in the oil temperature.
In a rotary damper of the type described in the Japanese publication, the open ends of the passages L1 and L2 place the left oil chamber R1 and the right oil chamber R2 in communication while bypassing the orifice 2a. When the vane is near one of the limits of its swing motion, the open end of the passage L1 and L2 closest to the vane is exposed to only a small volume of oil in a chamber defined between the side of the vane and the peripheral wall of the housing 1 that is closest to the vane.
As a consequence, when the side of the vane 2 is very near a peripheral wall of the housing 1 (i.e., when the vane is at one of the limits of its swing) the pressure-receiving space inside the chamber is extremely small as the vane starts moving back towards the center of the chamber, and the starting of this motion may thus not be smooth.
It has thus been suggested to provide a housing 1 with a left oil chamber R1 and a right oil chamber R2 divided by a vane 2 and having a configuration as shown in FIG. 3. This configuration includes front chambers A1 and A2, which remain on either side of the vane 2 and open to the oil passages even when the vane 2 moves close to the peripheral wall 1a of the housing 1 at the vane's maximum possible swing. These positions of the vane are shown in FIG. 3 by imaginary lines.
The volumes of the pressure-receiving spaces on either side of the vane 2 can thus be increased by making the front chambers A1 and A2 as large possible, which enhances the smooth starting of the vane's swinging movement as the vane begins to move away from one of its maximum position limits.
A rotary damper of the type shown in FIG. 3 is less than ideal however, in that it requires a larger amount of operating oil than other previous types. It would be desirable to reduce the amount of required operating oil, thereby reducing the cost of the products used in the damper.
In other words, the front chambers A1 and A2 of the rotary damper shown in FIG. 3 must be made large because the passages L1 and L2 (see FIG. 2) that place the left oil chamber R1 and the right oil chamber R2 into communication with each other open into the front chambers A1 and A2. In such a configuration, the front chambers A1 and A2 are formed such that the left oil chamber R1 and the right oil chamber R2 are widened in the direction of the vane's swing.
As a result, the rotary damper shown in FIG. 3 requires more oil than the one described in the Japanese publication. It would be desirable, though, to reduce the amount of operating oil, and thereby to reduce the overall weight and cost of the product.
This document describes an improved rotary damper for damping oscillations in the front tire of a moving motorcycle. A preferred embodiment described below allows a reduction in the overall weight and cost of the product, and thereby enhances its usability and versatility.